Fictivated glass and method of making

ABSTRACT

Silicate glasses that are fictivated and fast cooled and have high levels of intrinsic or “native” damage resistance. When ion exchanged, the silicate glasses described herein have a Vickers crack initiation threshold of at least 15 kgf and, in some embodiments, at least about 25 kgf.

This application claims the benefit of priority under 35 U.S.C. §119 ofU.S. Provisional Application Ser. No. 61/759061 filed on Jan. 31, 2013the content of which is relied upon and incorporated herein by referencein its entirety.

BACKGROUND

The disclosure relates to glasses that are capable of chemicalstrengthening by ion exchange and have intrinsic damage resistance. Moreparticularly, the disclosure relates to such glasses that are fastcooled and ion exchanged.

Ion exchangeable glass compositions offer advantages in glassmanufacturability and/or final properties compared to previous glasscompositions. Such glasses are used in applications such as, but notlimited to, cover glasses, windows, enclosures, and the like in avariety of electronic devices, including displays in entertainment andcommunication devices. Post-forming annealing processes tend to decreasethe damage resistance of such glasses.

SUMMARY

Silicate glasses that are fast cooled or fictivated and have high levelsof intrinsic or “native” damage resistance are provided. When ionexchanged, the silicate glasses described herein have a Vickers crackinitiation threshold of at least 15 kgf and, in some embodiments, atleast about 25 kgf.

Accordingly, one aspect of the disclosure is to provide silicate glasshaving a Vickers crack initiation threshold of at least 15 kgf. Thesilicate glass comprising: at least about 50 mol % SiO₂; at least about10 mol % R₂O, wherein R₂O comprises Na₂O; Al₂O₃, wherein −0.5 mol%≦Al₂O₃ (mol %)−R₂O (mol %)≦2 mol %; and B₂O₃, wherein B₂O₃ (mol %)−(R₂O(mol %)−Al₂O₃ (mol %))≧4.5 mol %. The silicate glass has a fictivetemperature that is greater than or equal to a temperature at which asuper-cooled liquid having the composition of the silicate glass is 10¹²Poise.

A second aspect of the disclosure is to provide a silicate glass havinga zircon breakdown temperature that is equal to the temperature at whichthe silicate glass has a viscosity in a range from about 30 kPoise toabout 40 kPoise, a Vickers crack initiation threshold of at least 15kgf, and a strain point. The silicate glass comprises: at least about 50mol % SiO₂; at least about 10 mol % R₂O, wherein R₂O comprises Na₂O;Al₂O₃, wherein Al₂O₃ (mol %)<R₂O (mol %); and B₂O₃, wherein B₂O₃ (mol%)−(R₂O (mol %)−Al₂O₃ (mol %))≧2 mol %, and wherein the silicate glasshas a fictive temperature that is greater than or equal to a temperatureat which a super-cooled liquid having the composition of the silicateglass is 10¹² Poise.

A third aspect of the disclosure is to provide a method of making asilicate glass having a Vickers crack initiation threshold of at least15 kgf. The silicate glass comprises: at least about 50 mol % SiO₂; atleast about 10 mol % R₂O, wherein R₂O comprises Na₂O; and B₂O₃, andwherein B₂O₃ (mol %)−(R₂O (mol %)−Al₂O₃ (mol %))≧2 mol %. The methodcomprises heating the silicate glass to a first temperature at which theglass has a viscosity in a range from about 10⁹ poise to about 10¹³poise and fast cooling the silicate glass from the first temperature toa second temperature, wherein the second temperature is less than astrain point of the silicate glass, and wherein the fast cooled silicateglass has a Vickers crack initiation threshold of at least 15 kgf.

These and other aspects, advantages, and salient features will becomeapparent from the following detailed description, the accompanyingdrawings, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot of average compressive stresses (CS) and depths oflayer (DOL) for the glasses listed in Tables 1 and 3a;

FIG. 2 is a plot of Vickers indentation thresholds obtained for ionexchanged fusion drawn glass and annealed glasses;

FIG. 3 is a plot of Vickers indentation thresholds obtained for ionexchanged fictivated and annealed samples having the glass compositionslisted in Tables 2 and 3b; and

FIG. 4 is a plot of Vickers indentation threshold and Young's modulus asa function of fictive temperature

DETAILED DESCRIPTION

In the following description, like reference characters designate likeor corresponding parts throughout the several views shown in thefigures. It is also understood that, unless otherwise specified, termssuch as “top,” “bottom,” “outward,” “inward,” and the like are words ofconvenience and are not to be construed as limiting terms. In addition,whenever a group is described as comprising at least one of a group ofelements and combinations thereof, it is understood that the group maycomprise, consist essentially of, or consist of any number of thoseelements recited, either individually or in combination with each other.Similarly, whenever a group is described as consisting of at least oneof a group of elements or combinations thereof, it is understood thatthe group may consist of any number of those elements recited, eitherindividually or in combination with each other. Unless otherwisespecified, a range of values, when recited, includes both the upper andlower limits of the range as well as any ranges therebetween. As usedherein, the indefinite articles “a,” “an,” and the correspondingdefinite article “the” mean “at least one” or “one or more,” unlessotherwise specified. It also is understood that the various featuresdisclosed in the specification and the drawings can be used in any andall combinations.

As used herein, the terms “glass” and “glasses” includes both glassesand glass ceramics. The terms “glass article” and “glass articles” areused in their broadest sense to include any object made wholly or partlyof glass and/or glass ceramic.

It is noted that the terms “substantially” and “about” may be utilizedherein to represent the inherent degree of uncertainty that may beattributed to any quantitative comparison, value, measurement, or otherrepresentation. These terms are also utilized herein to represent thedegree by which a quantitative representation may vary from a statedreference without resulting in a change in the basic function of thesubject matter at issue.

Referring to the drawings in general and to FIG. 1 in particular, itwill be understood that the illustrations are for the purpose ofdescribing particular embodiments and are not intended to limit thedisclosure or appended claims thereto. The drawings are not necessarilyto scale, and certain features and certain views of the drawings may beshown exaggerated in scale or in schematic in the interest of clarityand conciseness.

New ion exchangeable glass compositions are continually being developedto offer advantages in glass manufacturability and/or final propertiescompared to previous glass compositions. Such glasses are used inapplications such as, but not limited to, cover glasses, windows,enclosures, and the like in a variety of electronic devices, includingdisplays in entertainment and communication devices.

Presently, such glasses are typically based on two similar glasssystems: SiO₂—Al₂O₃—B₂O₃—MgO—Na₂O—P₂O₅ and SiO₂—Al₂O₃—MgO—Na₂O. Due tothe presence of boron or phosphorus in the glass, the first group ofglasses generally exhibits a high indentation threshold, as measured byVickers crack indentation experiments, after ion exchange. The presenceof boron and phosphorus generates an open structure (i.e., high molarvolume) in the glass.

In addition to compositional effects, open structures may also begenerated by thermal history. Described herein are ion exchangeablesilicate glasses in which high damage resistance/indentation thresholdis introduced through thermal treatment of ion exchanged glass sheets.The indentation threshold is improved by use of a post-formingfictivation process. As used herein, “fictivation” refers to imposing aspecified fictive temperature or thermal history on a glass throughappropriate heat treatment. The term “fast cooling” refers to cooling amaterial from a first temperature to a second temperature at a rate ofat least 5° C./s. Specifically, these terms, as used herein, refer tothe heating of the glass to a first temperature at which the glass has aviscosity of less than 10¹³ poise (P) followed by equilibrating theglass at the first temperature for a predetermined time period, and thenquickly quenching the glass to a second temperature below the strainpoint of the glass. In some embodiments, the glass is heated to a firsttemperature at which the glass has a viscosity in a range from about 10⁹poise to about 10¹³ poise followed by equilibration at the firsttemperature and rapid quenching to a second temperature below the strainpoint of the glass, and in other embodiments, fictivation includesheating the glass to a first temperature at which the viscosity of theglass is in a range from about 10⁹ poise to about 10¹¹ poise followed byequilibration at that temperature and rapid quenching to a secondtemperature that is below the strain point of the glass. In someembodiments, fictivation includes heating the glass to a firsttemperature at which the glass viscosity is about 10¹⁰ poise (P),followed by equilibrating the glass at that temperature for apredetermined time period, and then quickly quenching the glass to asecond temperature below the strain point of the glass. In someembodiments, the glass is fast cooled from the first temperature to asecond temperature which is about room temperature (25° C.±10° C.).

In contrast to fictivation, post-forming annealing processes tend todecrease the indentation threshold of glasses. By fast cooling, theindentation threshold may at least two times greater than that achievedby slowly cooled or annealed glasses. The temperature where fast coolingshould start to generate high indentation threshold corresponds to acritical viscosity at around 10⁹-10¹¹ poise, in some embodiments, around10⁹-10¹¹ poise, and in other embodiments, around 10¹⁰-10^(10.5) poise.

As used herein, the term “fictive temperature” refers to the temperaturewhich reflects the structural contribution to the enthalpy of the glass.The fictive temperature of a glass may be determined by calorimetricmethods, as described by Xiaoju Guo et al. in “Unified approach fordetermining the enthalpic fictive temperature of glasses with arbitrarythermal history,” (Journal of Non-Crystalline Solids 357 (2011) pp.3230-3236). The contents of which are incorporated herein by referencein their entirety. In the glasses described herein, the fictivetemperature is greater than or equal to the temperature at which theviscosity of the glass-forming liquid (i.e., a supercooled liquid of thesame composition) is 10¹² Poise.

Described herein are silicate glasses that are fast cooled or fictivatedand have high levels of intrinsic or “native” damage resistance. Whenion exchanged, the silicate glasses described herein have a Vickerscrack initiation threshold of at least 15 kgf and, in some embodiments,at least about 25 kgf.

In some aspects, the silicate glasses described herein comprise at leastabout 50 mol % SiO₂; at least about 10 mol % R₂O, where R₂O comprisesNa₂O; Al₂O₃, wherein −0.5 mol %≦Al₂O₃ (mol %)−R₂O (mol %)≦2 mol %; andB₂O₃, wherein B₂O₃ (mol %)−(R₂O (mol %)−Al₂O₃ (mol %))≧4.5 mol %. Insome embodiments, these glasses comprise at least about 50 mol % SiO₂,from about 9 mol % to about 22 mol % Al₂O₃, from about 3 mol % to about10 mol % B₂O₃, from about 9 mol % to about 20 mol % Na₂O, from 0 mol %to about 5 mol % K₂O, 0 mol %≦MgO≦6 mol %, and 0 mol %≦ZnO≦6 mol %. Inaddition, the glasses may optionally comprise at least one of CaO, BaO,and SrO, wherein 0 mol %≦CaO+SrO+BaO≦2 mol %.

In other embodiments, the silicate glass comprises at least about 50 mol% SiO₂, at least about 10 mol % R₂O, wherein R₂O comprises Na₂O; Al₂O₃,wherein Al₂O₃ (mol %)<R₂O (mol %); and B₂O₃, wherein B₂O₃ (mol %)−(R₂O(mol %)−Al₂O₃ (mol %))≧2 mol %. In some embodiments, these glassescomprise at least about 50 mol % SiO₂, from about 9 mol % to about 22mol % Al₂O₃, from about 3 mol % to about 10 mol % B₂O₃, from about 9 mol% to about 20 mol % Na₂O, from 0 mol % to about 5 mol % K₂O, from 0 mol% to about 6 mol % MgO; and from 0 mol % to about 6 mol % ZnO. Inaddition, the glasses may optionally comprise at least one of CaO, BaO,and SrO, wherein 0 mol %≦CaO+SrO+BaO≦2 mol %.

The silicate glasses described herein have a fictive temperature that isis greater than or equal to the temperature at which the viscosity ofthe glass-forming liquid (i.e., a supercooled liquid of the samecomposition) is 10¹² Poise. In some embodiments, the glass is fastcooled or fictivated from a first temperature above the anneal point ofthe glass to a temperature that is below the strain point of the glass.In some embodiments, the glass is fast cooled from the first temperatureto room temperature (25° C.±10° C.).

Only certain glass compositions exhibit indentation threshold valuesthat are most affected by thermal history. In the silicate glasscompositions described herein, SiO₂ serves as the primary glass-formingoxide. The concentration of SiO₂ in the glass should be sufficientlyhigh in order to provide the glass with sufficiently high chemicaldurability that is suitable for some applications such as, for exampletouch screen applications. However, the melting temperature (200 poisetemperature) of pure SiO₂ or glasses having high SiO₂ contents isconsidered too high, since defects such as fining bubbles may appearduring manufacture. Furthermore, SiO₂, compared to most oxides,decreases the level of compressive stress created by ion exchange.Accordingly, the silicate glasses described herein comprise at least 50mol % SiO₂. In some embodiments, these glasses comprise from about 66mol % to about 74 mol % SiO₂ and, in other embodiments from about 60 mol% to about 66 mol % SiO₂.

Alumina (Al₂O₃) can also serve as a glass former in these silicateglasses. Like SiO₂, alumina generally increases the viscosity of themelt. In addition, an increase in Al₂O₃ relative to the alkalis oralkaline earths generally results in improved durability of the glass.In some embodiments, −0.5 mol %≦Al₂O₃ (mol %)−R₂O (mol %)≦2 mol %. Inother embodiments, Al₂O₃ (mol %)<R₂O (mol %). The structural role of thealuminum ions depends on the glass composition. When the concentrationof alkali oxide(s) [R₂O] is greater than or equal to the concentrationof alumina [Al₂O₃], all aluminum is found in tetrahedral coordinationwith the alkali ions acting as charge-balancers. This is the case forsome of the glasses described herein. In other glasses, theconcentration of alkali oxide is less than the concentration of aluminumions, in which case divalent cation oxides (RO) can also charge balancetetrahedral aluminum to various extents. While elements such as calcium,zinc, strontium, and barium behave equivalently to two alkali ions, thehigh field strength of magnesium ions cause them to not fully chargebalance aluminum in tetrahedral coordination, resulting in formation offive- and six-fold coordinated aluminum. Generally, Al₂O₃ plays anextremely important role in ion-exchangeable glasses, since it enables astrong network backbone (i.e., high strain point) while allowing forrelatively fast diffusivity of alkali ions. High Al₂O₃ concentrations,however, generally lower the liquidus viscosity. Al₂O₃ concentrationtherefore needs to be kept in a reasonable range. In some embodiments,the silicate glasses described herein comprise from about 9 mol % toabout 22 mol % Al₂O₃ and, in other embodiments, the glasses comprisefrom about 12 mol % to about 22 mol % Al₂O₃.

The silicate glasses described herein comprise at least about 10 mol %alkali metal oxides R₂O, wherein R₂O includes Na₂O. Alkali metal oxides(Li₂O, Na₂O, K₂O, Rb₂O, and Cs₂O) serve as aids in achieving low meltingtemperature and low liquidus temperatures of the glass. However, theaddition of alkali oxide(s) dramatically increases the coefficient ofthermal expansion (CTE) and lowers the chemical durability of the glass.The silicate glasses described herein, in some embodiments, comprisefrom about 9 mol % to about 20 mol % Na₂O and, in other embodiments,from about 10 mol % to about 20 mol % Na₂O. The glasses may alsocomprise from 0 mol % to about 5 mol % K₂O. To perform ion exchange, thepresence of a small alkali oxide such as Li₂O and Na₂O is required toexchange with larger alkali ions (e.g., K⁺) from a salt bath or otherion exchange medium. Three types of ion exchange can generally becarried out: Na⁻-for-Li⁺ exchange, which results in a deep depth oflayer but low compressive stress; K⁺-for-Li⁺ exchange, which results ina small depth of layer but a relatively large compressive stress; andK⁺-for-Na⁺ exchange, which results in intermediate depth of layer andcompressive stress. A sufficiently high concentration of the smallalkali oxide is necessary to produce a large compressive stress in theglass, since compressive stress is proportional to the number of alkaliions that are exchanged out of the glass. In some of the exampleglasses, a small amount of K₂O is introduced into the glass to improvediffusivity and lowers the liquidus temperature, but it generallyincreases the CTE and decreases CS. Thus, the potassium concentration ofthe glass is kept at a very low level (e.g., ≦5 mol %) and, in certainembodiments, the glass is free of potassium. In certain embodiments, thesilicate glass is free of lithium.

Divalent cation oxides (such as alkaline earth oxides and ZnO) alsoimprove the melting behavior of the glass. With respect to ion exchangeperformance, however, the presence of divalent cations acts to decreasealkali mobility. The negative effect of divalent cations on ion exchangeperformance is especially pronounced with the larger divalent cations.Furthermore, the smaller divalent cation oxides (e.g., MgO, ZnO)generally help increase the compressive stress of the glass more thanthe larger divalent cations. Hence, MgO and ZnO offer several advantageswith respect to improved stress relaxation while minimizing the adverseeffects on alkali diffusivity. However, when the concentrations of MgOand ZnO in the glass are high, these oxides are prone to form forsterite(Mg₂SiO₄) and gahnite (ZnAl₂O₄) or willemite (Zn₂SiO₄), respectively,thus causing the liquidus temperature of the glass to rise very steeplywhen the MgO and ZnO contents are above certain levels. In someembodiments, the silicate glass comprises at least about 0.1 mol % of atleast one of MgO and ZnO, and in some embodiments, 0 mol %≦MgO≦6 mol %and 0 mol %≦ZnO≦6 mol %. In some embodiments, either MgO or ZnO as theonly divalent cation oxide in the glass; i.e., the glass is free ofother alkaline earth oxides (CaO, BaO, SrO). In other embodiments,however, the glass may include at least one of CaO, BaO, and SrO,wherein 0 mol %≦CaO+SrO+BaO≦2 mol %.

The glasses described herein comprise B₂O₃ and, in some embodiments, theglass comprises from about 3 mol % to about 10 mol % B₂O₃. The additionof B₂O₃ and P₂O₅ improve the damage resistance of the glass. When boronis not charge balanced by alkali oxides or divalent cation oxides, itwill be in trigonal coordination state, and thus open up the structureand provide greater damage resistance. The network around these trigonalcoordinated borons is not as rigid as tetrahedrally coordinated ones,the bonds are floppy, and therefore the glasses can tolerate somedeformation before crack formation. In some embodiments, the silicateglass comprises greater than 4.5 mol % B₂O₃ in which boron cations arethree-fold coordinated. In other embodiments, the glass comprisesgreater than 2 mol % B₂O₃ in which boron cations are three-foldcoordinated and, in some embodiments the silicate glass comprises fromabout 2 mol % to about 4.5 mol % of three-fold coordinated boroncations. In certain embodiments, B₂O₃ (mol %)−(R₂O (mol %)−Al₂O₃ (mol%))≧2 mol %, and some embodiments, B₂O₃ (mol %)−(R₂O (mol %)−Al₂O₃ (mol%))≦4.5 mol %. In some embodiments, B₂O₃ (mol %)−(R₂O (mol %)−Al₂O₃ (mol%))≧4.5 mol %. Furthermore, both boron and phosphorus decrease themelting viscosity and effectively help to suppress zircon breakdownviscosity.

Unlike B₂O₃, P₂O₅ can improve the diffusivity of alkali cations anddecrease ion exchange times. In some embodiments, the glasses describedherein, P₂O₅ may replace at least a portion of B₂O₃ in the glass suchthat 4.5 mol %≦B₂O₃ (mol %)+P₂O₅ (mol %)≦10 mol %. However, the floppystructure formed by boron and phosphorus sacrifice some compressivestress capability where the effect from P₂O₅ is also pronounced. Thecoordination number change of B₂O₃ on fictive temperature is the sourceof the variation of indentation threshold with thermal history. Thecompositions included herein are boron containing glasses. Trigonallycoordinated boron in glasses with higher fictive temperatures willpartially convert to tetrahedral coordinated when the fictivetemperature of the glass decreases. During annealing or heat treatment,the fictive temperature of the glass will be reduced, and the amount oftrigonal coordinated boron will therefore decrease. If this change isdramatic, the level of trigonally coordinated boron will not besufficient to sustain the open glass structure. FIG. 4, which is a plotof Vickers indentation threshold and Young's modulus as a function offictive temperature, shows that the elastic modulus increases and theindentation threshold decreases as the fictive temperature is lowered.As the fictive temperature decreases, the glass becomes denser and lessable to accommodate mechanical insult. As seen in FIG. 4, theindentation threshold can be dramatically reduced as a result of adecrease in fictive temperature.

In some embodiments, the silicate glasses described herein may furthercomprise at least one transition metal oxide colorant comprising atleast one of V₂O₅, NiO, CuO, Cr₂O₃, MnO₂, Fe₂O₃, Co₃O₄, Nb₂O₅, and TiO₂.In such instances, the transition metal oxide colorants may comprise upto 6 mol % of the glass; i.e., 0 mol %≦V₂O₅≦6 mol %, 0 mol %≦NiO≦6 mol%, 0 mol %≦CuO≦6 mol %, 0 mol %≦Cr₂O₃≦6 mol %, 0 mol %≦MnO₂≦6 mol %, 0mol %≦Fe₂O₃≦6 mol %, 0 mol %≦Co₃O₄≦6 mol % 0 mol %≦Nb₂O₅≦6 mol %, and 0mol %≦TiO₂≦6 mol %.

In some aspects, the glasses described herein are ion exchanged by thosemeans known in the art such as, for example immersion in a molten saltbath containing salts of the cation that is to replace the cation in theglass. Cations—typically monovalent alkali metal cations that which arepresent in these glasses are replaced with larger cations—typicallymonovalent alkali metal cations, although other cations such as Ag⁻ orTl⁻ may be used—having the same valence or oxidation state. Thereplacement of smaller cations with larger cations creates a surfacelayer that is under compression, or compressive stress CS. This layerextends from the surface of the glass into the interior or bulk of theglass to a depth of layer DOL. The compressive stress in the surfacelayers of the glass are balanced by a tensile stress, or central tensionCT, in the interior or inner region of the glass. The ion exchangedglasses, in some embodiments, have a surface layer under a compressivestress of at least about 800 MPa and, in certain embodiments, at least900 MPa, wherein the layer extends to a depth of layer of at least about45 μm and, in some embodiments, at least about 30 μm. Compressive stressand depth of layer are measured using those means known in the art. Suchmeans include, but are not limited to measurement of surface stress(FSM) using commercially available instruments such as the FSM-6000,manufactured by Luceo Co., Ltd. (Tokyo, Japan), or the like. Methods ofmeasuring compressive stress and depth of layer are described in ASTM1422C-99, entitled “Standard Specification for Chemically StrengthenedFlat Glass,” and ASTM 1279.19779 “Standard Test Method forNon-Destructive Photoelastic Measurement of Edge and Surface Stresses inAnnealed, Heat-Strengthened, and Fully-Tempered Flat Glass,” thecontents of which are incorporated herein by reference in theirentirety. Surface stress measurements rely upon the accurate measurementof the stress optical coefficient (SOC), which is related to thestress-induced birefringence of the glass. SOC in turn is measured bythose methods that are known in the art, such as fiber and four pointbend method, both of which are described in ASTM standard C770-98(2008), entitled “Standard Test Method for Measurement of GlassStress-Optical Coefficient,” the contents of which are incorporatedherein by reference in their entirety, and a bulk cylinder method.

The ion exchanged glasses described herein possess a degree of intrinsicdamage resistance (IDR), which may be characterized by the Vickers crackinitiation threshold of the ion exchanged glass. In some embodiments,the ion exchanged glass has a Vickers crack initiation threshold of atleast about 15 kgf. In some embodiments, the ion exchanged glass has aVickers crack initiation threshold in a range from about 20 kgf to about30 kgf and, in other embodiments, at least about 25 kgf. The Vickerscrack initiation threshold measurements described herein are performedby applying and then removing an indentation load to the glass surfaceat a rate of 0.2 mm/min. The maximum indentation load is held for 10seconds. The crack initiation threshold is defined at the indentationload at which 50% of 10 indents exhibit any number of radial/mediancracks emanating from the corners of the indent impression. The maximumload is increased until the threshold is met for a given glasscomposition. All indentation measurements are performed at roomtemperature in 50% relative humidity.

Non-limiting examples of glass compositions in which the post-ionexchange Vickers indentation threshold is greatly affected by fastcooling and the respective physical properties of these glasses arelisted in Table 1. All glasses were fusion formed and fast cooled. Thecompositions were analyzed using x-ray fluorescence and/or opticalemission spectrometry (ICP-OES) plus FES. Anneal and strain points weredetermined by beam bending viscometry and softening points weredetermined by parallel plate viscometry. The coefficient of thermalexpansion (CTE) is the average value between room temperature and 300°C. Elastic moduli were determined by resonant ultrasound spectroscopy.Refractive index is stated for 589.3 nm. Stress optic coefficient (SOC)was determined by the diametral compression method.

Table 2 lists additional compositions in which the Vickers indentationthreshold of ion exchanged glass was greatly affected by fast cooling.All of the glasses listed in Table 2 were fusion formed and fictivated,and the compositions reported were either batched of analyzed usingeither x-ray fluorescence or ICP.

TABLE 1 Compositions and physical properties of fusion drawn fast cooledglasses. Composition (mol %) Ref. A Glass 2 Glass 3 Glass 4 Glass 5Glass 6 Ref. B Al₂O₃ 13.9 13.6 13.3 13.3 13.1 12.9 12.7 Na₂O 13.6 13.613.6 13.7 13.6 13.6 13.6 MgO 2.4 2.4 2.4 2.4 2.3 2.4 2.4 B₂O₃ 5.1 4.94.6 4.0 4 3.8 3.7 SiO₂ 64.9 65.4 65.9 66.5 66.7 67.1 67.5 SnO₂ 0.07 0.090.09 0.09 0.09 0.09 0.09 Anneal Pt. (° C.): 625 626 628 629 630 632 631Strain Pt. (° C.): 572 574 574 576 577 579 578 Softening Pt. (° C.):893.4 896 899.3 900.4 903 902.4 903.1 Density (g/cm³): 2.39 2.391 2.3922.392 2.393 2.393 2.393 CTE (×10⁻⁷/° C.): 75.1 74.8 74.6 75 75.5 75.875.1 Poisson's Ratio: 0.22 0.218 0.22 0.217 0.221 0.213 0.2 ShearModulus (Mpsi): 4.047 4.077 4.086 4.094 4.105 4.125 4.157 Young'sModulus (Mpsi): 9.873 9.934 9.968 9.963 10.024 10.004 9.975 RefractiveIndex: 1.497 1.497 1.496 1.496 1.496 1.496 1.496 Stress opticcoefficient 32.7 32.5 32.4 32.3 32.2 32.0 31.9

TABLE 2 Compositions and physical properties of fast cooled, fictivatedglasses. Composition (mol %) Glass 8 Glass 9 Glass 10 Glass 11 Glass 12SiO₂ 65.74 65.86 64.5 64.5 64.5 Al₂O₃ 13.57 13.56 14.75 14.75 14.75 B₂O₃5.63 5.25 6 5.5 5 Na₂O 14.05 14.32 13.55 13.55 13.55 K₂O 0.10 0.10 0.20.2 0.2 MgO 0.77 0.76 0 0 0 CaO 0.04 0.04 0.05 0.05 0.05 ZnO 0.00 0.00 11.5 2 SnO₂ 0.10 0.10 0.07 0.07 0.07 Composition (mol %) Glass 13 Glass14 Glass 15 Glass 16 Glass 17 SiO₂ 64.5 64.5 64.5 64.5 64.5 Al₂O₃ 14.7514.75 14.75 14.75 14.75 B₂O₃ 4.5 4 7 6 5.5 Na₂O 13.55 13.55 13.55 13.5513.55 K₂O 0.2 0.2 0.2 0.2 0.2 MgO 0 0 0 1 1.5 CaO 0.05 0.05 0.05 0.050.05 ZnO 2.5 3 0 0 0 SnO₂ 0.07 0.07 0.07 0.07 0.07 Composition (mol %)Glass 18 Glass 19 Glass 20 Glass 21 Glass 22 SiO₂ 64.5 64.5 64.5 64.4464.53 Al₂O₃ 14.75 14.75 14.75 13.99 13.99 B₂O₃ 5 4.5 4 7.04 6.60 Na₂O13.55 13.55 13.55 13.83 13.71 K₂O 0.2 0.2 0.2 0.51 0.50 MgO 2 2.5 3 0.010.49 CaO 0.05 0.05 0.05 0.06 0.06 SnO₂ 0.07 0.07 0.07 0.10 0.10Composition (mol %) Glass 23 Glass 24 Glass 25 Glass 26 Glass 27 SiO₂64.32 64.76 64.53 64.33 65.00 Al₂O₃ 14.00 13.97 13.98 14.01 13.50 B₂O₃6.15 5.57 5.06 4.58 3.00 Na₂O 13.82 13.56 13.74 13.82 15.40 K₂O 0.510.50 0.51 0.51 0.10 MgO 1.01 1.45 2.00 2.57 3.00 CaO 0.06 0.06 0.06 0.060.00 SnO₂ 0.10 0.10 0.10 0.10 0.08 Composition (mol %) Glass 28 Glass 29Glass 30 Glass 31 Glass 32 SiO₂ 65.00 65.00 65.00 65.00 65.00 Al₂O₃14.00 14.25 14.50 14.75 15.00 B₂O₃ 3.00 3.00 3.00 3.00 3.00 Na₂O 14.9014.65 14.40 14.15 13.90 K₂O 0.10 0.10 0.10 0.10 0.10 MgO 3.00 3.00 3.003.00 3.00 CaO 0.00 0.00 0.00 0.00 0.00 SnO₂ 0.08 0.08 0.08 0.08 0.08

Table 3a lists ion exchange properties of glasses 2-6 from Table 1. Ionexchange (“IX” in Tables 3a and 3b) was performed for fusion formedglasses (“as-drawn” in Table 3a) and for glasses annealed at 600° C. for20 hours, and at 630° C. for 2 hours. The compressive stress (CS) anddepth of layer (DOL) were obtained as a result of treatment of annealedsamples in KNO₃ (refined grade) at 410° C. for a time sufficient toobtain a depth of layer of about 50 μm. The average compressive stresses(CS) and depths of layer (DOL) for the glasses listed in Tables 1 and 3aare plotted in FIG. 1. Table 3b lists ion exchange properties ofselected silicate glasses from Table 2 which were either annealed orfictivated as described herein.

TABLE 3a Ion exchange properties of silicate glasses listed in Tables 1and 2. 4318 Glass 2 Glass 3 Glass 4 Glass 5 Glass 6 2320 Annealed 20 hrat 600° C. CS (MPa) 1084 1082 1088 1080 1095 1090 1090 DOL (μm) 45.245.2 45 46.9 45.3 47.2 46.9 IX time (hr) 18 17.3 16.4 15.6 16.4 15.615.6 Annealed 20 hr at 630° C. CS (MPa) 1038 1023 1016 1035 1040 10331032 DOL (μm) 46.7 47.5 48 46.7 47.5 48.1 48.4 IX time (hr) 15.1 14.613.8 13.2 13.8 13.2 13.2 As-Drawn CS (MPa) 893 929 903.2 893 882.5 885877 DOL (μm) 52.1 47.6 51.6 52.1 53 53.8 54.4 IX time (hr) 11.8 11.310.6 10.6 10 10 10

TABLE 3b Ion exchange properties of fictivated and annealed silicateglasses listed in Table 2. Glass Glass Glass Glass Glass Glass 14 15 1617 18 19 Annealed CS (MPa) 897.6 952.3 972.9 1002.4 1026.2 1032.9 DOL(μm) 42.8 40.5 39.4 38.2 37.5 36.0 IX temp. (° C.) 410 410 410 410 410410 IX time (h) 8 8 8 8 8 8 Fictivated CS (MPa) 809.7 861.3 883.2 912.1930.8 938.1 DOL (μm) 45.5 42.4 40.1 38.3 37.3 36.8 IX temp. (° C.) 390390 390 390 390 390 IX time (h) 8 8 8 8 8 8

The thermal history dependence of Vickers indentation threshold for theglasses listed in Tables 1 and 3a was studied. Vickers indentationthresholds obtained for fusion drawn glass and annealed glasses arecompared in FIG. 2. The glass compositions are listed in Table 1 and thecorresponding compressive stresses and depths of layer are listed inTable 3. Four samples were tested for each condition. Indentationthreshold values measured for ion exchanged samples having a depth oflayer in the 40-50 μm range. The effect of thermal history onindentation threshold was studied for annealed and fusion formedsamples. The glasses were fictivated or fast cooled from a temperaturethat was about 60° C. to 70° C. higher than their respective annealpoints. The as-formed annealed and fictivated glasses were ion exchangedin a potassium nitrate salt bath. All ion exchanged glasses from thesetwo different approaches were studied for indentation threshold. Thefictivated glasses (labeled “a” in FIG. 2) exhibited higher Vickersindentation thresholds than the annealed glasses.

Vickers indentation thresholds obtained for ion exchanged fictivated andannealed samples having the glass compositions listed in Tables 2 and 3bare plotted in FIG. 3. Fictivation results in higher indentationthresholds for all compositions studied.

In some aspects, the silicate glasses described herein have a zirconbreakdown temperature that is equal to the temperature at which theviscosity of the glass is in a range from about 30 kPoise to about 35kPoise, in some embodiments, in a range from about 70 kPoise to about 80kPoise, and, in a particular embodiment, from 30 kPoise to about 35kPoise. As used herein, the term “zircon breakdown temperature” or“T^(breakdown)” refers to the temperature at which zircon—which iscommonly used as a refractory material in glass processing andmanufacture—breaks down to form zirconia and silica. In isoviscousprocesses such as fusion, the highest temperature experienced by theglass corresponds to a particular viscosity of the glass. For example,“T^(35kP)” refers to the temperature at which the glass has a viscosityof 35 kilopoise (kP). The difference between the breakdown temperatureand the temperature corresponding to 35,000 poise viscosity is definedas the breakdown margin T^(margin), where:T^(margin)=T^(breakdown)−T^(35kp). When the breakdown margin T^(margin)is negative, zircon will breakdown to form zirconia defects at somelocation on the isopipe. When T^(margin) is zero, it is still possiblethat temperature excursions could cause zircon breakdown to occur. It istherefore desirable not only to make the breakdown margin positive, butto maximize T^(margin) as much as possible while being consistent withall the other attributes that must be maintained in the final glassproduct. In some embodiments, the silicate glasses contain less thanabout one inclusion per kilogram of silicate glass, the inclusion havinga diameter of at least 50 μm.

A method of making the silicate glasses described hereinabove is alsoprovided. The silicate glass has a Vickers crack initiation threshold ofat least 15 kgf and, comprises: at least about 50 mol % SiO₂; at leastabout 10 mol % R₂O, wherein R₂O comprises Na₂O; Al₂O₃; and B₂O₃, andwherein B₂O₃ (mol %)−(R₂O (mol %)−Al₂O₃ (mol %))≧2 mol %. The glass isfirst heated to a first temperature that is greater than the annealpoint of the glass, and then fast cooled at a rate of at least about 5°C./s from the first temperature to a second temperature that is lessthan the strain point of the glass. In some embodiments, the methodfurther includes providing the silicate glass by slot-drawing,fusion-drawing, rolling, or float processing. In certain embodiments,the method further includes ion exchanging the fast cooled silicateglass to form a layer under a compressive stress, the layer extendingfrom a surface of the silicate glass into the silicate glass to a depthof layer.

While typical embodiments have been set forth for the purpose ofillustration, the foregoing description should not be deemed to be alimitation on the scope of the disclosure or appended claims.Accordingly, various modifications, adaptations, and alternatives mayoccur to one skilled in the art without departing from the spirit andscope of the present disclosure or appended claims.

1. A silicate glass, the silicate glass having a Vickers crackinitiation threshold of at least 15 kgf, and a strain point, thesilicate glass comprising: at least about 50 mol % SiO₂; at least about10 mol % R₂O, wherein R₂O comprises Na₂O; Al₂O₃, wherein −0.5 mol%≦Al₂O₃ (mol %)−R₂O (mol %)≦2 mol %; and B₂O₃, wherein B₂O₃ (mol %)−(R₂O(mol %)−Al₂O₃ (mol %))≧4.5 mol %, wherein the silicate glass has afictive temperature that is greater than or equal to a temperature atwhich a super-cooled liquid having a composition of the silicate glassis 10¹² Poise.
 2. The silicate glass of claim 1, wherein the silicateglass has a Vickers crack initiation threshold of at least about 25 kgf.3. The silicate glass of claim 1, wherein the silicate glass has a layerunder a compressive stress of at least about 800 MPa, the layerextending from a surface of the silicate glass into the silicate glassto a depth of layer of at least about 45 μm.
 4. The silicate glass ofclaim 1, wherein the silicate glass comprises from about 60 mol % toabout 66 mol % SiO₂.
 5. The silicate glass of claim 1, wherein thesilicate glass comprises at least about 0.1 mol % of at least one of MgOand ZnO.
 6. The silicate glass of claim 1, wherein the silicate glasscomprises greater than 4.5 mol % B₂O₃ in which boron cations arethree-fold coordinated.
 7. The silicate glass of claim 1, wherein thesilicate glass comprises: at least about 50 mol % SiO₂, from about 12mol % to about 22 mol % Al₂O₃; from about 4.5 mol % to about 10 mol %B₂O₃; from about 10 mol % to about 20 mol % Na₂O; from 0 mol % to about5 mol % K₂O; 0 mol %≦MgO≦6 mol %; 0 mol %≦ZnO≦6 mol %; and, optionally,at least one of CaO, BaO, and SrO, wherein 0 mol %≦CaO+SrO+BaO≦2 mol %.8. The silicate glass of claim 1, further comprising at least onetransition metal colorant, the transition metal oxide colorantcomprising at least one of V₂O₅, NiO, CuO, Cr₂O₃, MnO₂, Fe₂O₃, Co₃O₄,Nb₂O₅, and TiO₂.
 9. The silicate glass of claim 8, wherein 0 mol%≦V₂O₅≦6 mol %, 0 mol %≦NiO≦6 mol %, 0 mol %≦CuO≦6 mol %, 0 mol%≦Cr₂O₃≦6 mol %, 0 mol %≦MnO₂≦6 mol %, 0 mol %≦Fe₂O₃≦6 mol %, 0 mol%≦Co₃O₄≦6 mol % 0 mol %≦Nb₂O₅≦6 mol %, and 0 mol %≦TiO₂≦6 mol %.
 10. Thesilicate glass of claim 1, further including P₂O₅, wherein 4.5 mol%≦B₂O₃ (mol %)+P₂O₅ (mol %)≦10 mol %.
 11. The silicate glass of claim 1,wherein the silicate glass is fast cooled from a first temperature atwhich the glass has a viscosity in a range from about 10⁹ poise to about10¹³ poise to a second temperature that is below the strain point. 12.The silicate glass of claim 1, wherein the silicate glass forms at leasta portion of a cover plate, a touch screen, a watch crystal, a solarconcentrator, a window, a screen, or a container.
 13. A silicate glass,the silicate glass having a zircon breakdown temperature that is equalto the temperature at which the silicate glass has a viscosity in arange from about 30 kPoise to about 40 kPoise, a Vickers crackinitiation threshold of at least 15 kgf, and a strain point, thesilicate glass comprising: at least about 50 mol % SiO₂; at least about10 mol % R₂O, wherein R₂O comprises Na₂O; Al₂O₃, wherein Al₂O₃ (mol%)<R₂O (mol %); and B₂O₃, wherein B₂O₃ (mol %)−(R₂O (mol %)−Al₂O₃ (mol%))≧2 mol %, wherein the silicate glass has a fictive temperature thatis greater than or equal to a temperature at which a super-cooled liquidhaving a composition of the silicate glass is 10¹² Poise.
 14. Thesilicate glass of claim 13, wherein the silicate glass has a layer undera compressive stress of at least about 800 MPa, the layer extending froma surface of the silicate glass into the silicate glass to a depth oflayer of at least about 45 μm.
 15. The silicate glass of claim 13,wherein the Vickers crack initiation threshold is at least about 25 kgf.16. The silicate glass of claim 13, wherein the silicate glass comprisesfrom about 3 mol % to about 4.5 mol % B₂O₃ in which boron cations arethree-fold coordinated.
 17. The silicate glass of claim 13, wherein B₂O₃(mol %)−(R₂O (mol %)−Al₂O₃ (mol %))≦4.5 mol %
 18. The silicate glass ofclaim 13, wherein the silicate glass comprises from about 66 mol % toabout 74 mol % SiO₂.
 19. The silicate glass of claim 13, wherein thesilicate glass comprises at least about 0.1 mol % of at least one of MgOand ZnO.
 20. The silicate glass of claim 13, wherein the glasscomprises: at least about 50 mol % SiO₂, from about 9 mol % to about 22mol % Al₂O₃; from about 3 mol % to about 10 mol % B₂O₃; from about 9 mol% to about 20 mol % Na₂O; from 0 mol % to about 5 mol % K₂O; 0 mol%≦MgO≦6 mol %; 0 mol %≦ZnO≦6 mol %; and, optionally, at least one ofCaO, BaO, and SrO, wherein 0 mol %≦CaO+SrO+BaO≦2 mol %.
 21. The silicateglass of claim 13, wherein the silicate glass contains less than aboutone inclusion per kilogram of silicate glass, the inclusion having adiameter of at least 50 μm.
 22. The silicate glass of claim 13, furthercomprising at least one transition metal colorant, the transition metaloxide colorant comprising at least one of V₂O₅, NiO, CuO, Cr₂O₃, MnO₂,Fe₂O₃, Co₃O₄, Nb₂O₅, and TiO₂.
 23. The silicate glass of claim 22,wherein 0 mol %≦V₂O₅≦6 mol %, 0 mol %≦NiO≦6 mol %, 0 mol %≦CuO≦6 mol %,0 mol %≦Cr₂O₃≦6 mol %, 0 mol %≦MnO₂≦6 mol %, 0 mol %≦Fe₂O₃≦6 mol %, 0mol %≦Co₃O₄≦6 mol % 0 mol %≦Nb₂O₅≦6 mol %, and 0 mol %≦TiO₂≦6 mol %. 24.The silicate glass of claim 13, wherein the silicate glass is fastcooled from a first temperature at which the glass has a viscosity in arange from about 10⁹ poise to about 10¹³ poise to a second temperaturethat is below the strain point.
 25. The silicate glass of claim 13,wherein the silicate glass forms at least a portion of a cover plate, atouch screen, a watch crystal, a solar concentrator, a window, a screen,or a container.
 26. A method of making a silicate glass having a Vickerscrack initiation threshold of at least 15 kgf and comprising: at leastabout 50 mol % SiO₂; at least about 10 mol % R₂O, wherein R₂O comprisesNa₂O; Al₂O₃; and B₂O₃, and wherein B₂O₃ (mol %)−(R₂O (mol %)−Al₂O₃ (mol%))≧2 mol %; the method comprising: a. heating the silicate glass to afirst temperature, the first temperature being greater than an annealpoint of the silica glass; and b. fast cooling the silicate glass from afirst temperature at which the glass has a viscosity in a range fromabout 10⁹ poise to about 10¹³ poise to a second temperature, the secondtemperature being less than a strain point of the silicate glass,wherein the fast cooled silicate glass has a Vickers crack initiationthreshold of at least 15 kgf.
 27. The method of claim 26, furthercomprising providing the silicate glass by slot-drawing, fusion-drawing,rolling, or float processing.
 28. The method of claim 26, furthercomprising ion exchanging the silicate glass to form a layer under acompressive stress, the layer extending from a surface of the silicateglass into the silicate glass to a depth of layer.
 29. The method ofclaim 28, wherein the compressive stress is at least about 800 MPa. 30.The method of claim 28, wherein the depth of layer is at least about 45μm.
 31. The method of claim 26, wherein the Vickers crack initiationthreshold of at least about 25 kgf.
 32. The method of claim 26, whereinthe silicate glass comprises: at least about 50 mol % SiO₂, from about12 mol % to about 22 mol % Al₂O₃; from about 4.5 mol % to about 10 mol %B₂O₃; from about 10 mol % to about 20 mol % Na₂O; from 0 mol % to about5 mol % K₂O; 0 mol %≦MgO≦6 mol %; 0 mol %≦ZnO≦6 mol %; and, optionally,at least one of CaO, BaO, and SrO, wherein 0 mol %≦CaO+SrO+BaO≦2 mol %.33. The method of claim 26, wherein the glass comprises: at least about50 mol % SiO₂, from about 9 mol % to about 22 mol % Al₂O₃; from about 3mol % to about 10 mol % B₂O₃; from about 9 mol % to about 20 mol % Na₂O;from 0 mol % to about 5 mol % K₂O; 0 mol %≦MgO≦6 mol %; 0 mol %≦ZnO≦6mol %; and, optionally, at least one of CaO, BaO, and SrO, wherein 0 mol%≦CaO+SrO+BaO≦2 mol %.
 34. The method of claim 33, wherein the silicateglass has a zircon breakdown temperature that is equal to thetemperature at which the silicate glass has a viscosity in a range fromabout 30 kPoise to about 40 kPoise.
 35. The method of claim 26, whereinthe second temperature is about 25° C.±15° C.
 36. The method of claim26, wherein the silicate glass has a fictive temperature that is greaterthan or equal to a temperature at which a super-cooled liquid having acomposition of the silicate glass is 10¹² Poise.